The present invention relates to a centralized data communications system in which a plurality of groups of remote stations communicate with a central station over a respective plurality of communications channels each of which is shared by all the remote stations of a group. In a preferred arrangement of the system, data communicated from the remote stations to the central station is representative of sensed current in an electrical path which is used, together with data representing the voltage on the electrical path, by the central station to indicate energy consumption for information and billing purposes.
Various types of centralized data communications systems have been proposed in which a plurality of remote stations are addressed by a central station over one or more communications channels for the purposes of receiving data from or transmitting data to the remote stations. Generally speaking, the type of addressing which is employed is quite complex requiring sophisticated apparatus at both the central and remote stations. The complexity of this apparatus naturally decreases its reliability and increases its cost, limiting widespread use of centralized data communications systems.
Accordingly, one object of the present invention is to provide a relatively simple, reliable and low-cost data communications system in which a central station tone addresses a plurality of remote stations, each containing a plurality of information channels which may send data to or receive data from the central station. Each remote station contains apparatus therein for counting the number of tones on a communications channel connecting it to the central station and connecting one of the information channels to the communications channel only when the number of counted tones falls within a numerical range of tones assigned thereto. In addition, each remote station contains apparatus for sequentially connecting the information channels to the communications channel as tones within the predetermined numerical range assigned to remote station are counted. This type of addressing provides a centralized data communications system which is both simple and reliable, while considerably reducing its cost. The simplicity of construction of the remote stations also allows them to be constructed as low-cost modules which may be powered solely by the addressing tones.
An additional object of the invention is the provision of a centralized data communications system which is flexible and versatile, and which can be easily adapted to accurately take various output measurements from various types of sensors which may be connected to information channels at the remote stations.
An additional object of the invention is the provision of a centralized data communications system having a high degree of measurement accuracy which is achieved by calibrating the output of a remote station sensor. This is accomplished by first receiving and storing at a central station output calibration data from the sensor when measuring a parameter under known conditions. This calibration data is subtracted from output data of the sensor when measuring a parameter under unknown conditions, thus providing data that has been normalized to the known conditions.
An additional object of the invention is the provision of an automatic digital gain control circuit which is used at the central station of a centralized data communications system to adjust the level of an incoming signal to be within a predetermined measurement range of the central station equipment.
An additional object of the invention is the provision of a simple and low cost remote station module which is connected to a central station and used to monitor energy consumption or other parameters, which module contains unique circuitry for decoding and responding to tones emitted by the central station during addressing.
An additional object of the invention is the provision of a centralized data communications system which, with low cost sensors, is capable of measuring temperature, fluid flow, power and BTU consumption at a remote station with a high degree of accuracy.
An additional object of the invention is the provision of a centralized data communications system capable of controlling operations at an addressed remote station by sending tone control signals thereto.
The present invention also relates to a system for monitoring of energy consumption in an electrical path at a remote station. At present, there are many electrical installations such as in commercial buildings, apartments, condominiums, etc. where a single utility meter is provided at an electrical service entrance. With this arrangement, individual energy consumption in the apartments or other units of the building cannot be individually monitored or billed. This tends to promote waste as the occupants of the apartments have no individual control over total energy consumption and consequently little or no economic incentive to conserve energy.
Accordingly, an additional object of the invention is the provision of an energy management system which can be installed in a new or existing building not having individual unit metering to monitor and provide an indication of the individual energy consumption in each unit. Monitoring of the energy consumption enables the provision of an internal billing system for the building in which energy consumed by each unit can be individually metered and billed. In the system of the invention each unit contains at least one remote station communicating with a computer controlled central station over a communications channel. Each remote station includes at least one information channel which is connected to a current sensor which monitors the current passing through an input electrical path providing electrical service to the unit. The central station computer receives data from the current sensor representating current consumption and data representing voltage in the electrical path and calculates power, storing and processing it to provide a periodic indication of energy consumption which may be used for information or billing purposes. Thus, even though a building may not have individual electrical metering of each of the units, the system of the invention provides this function.
An additional object of the invention is to provide a unique power calculation circuit for calculating power existing in an electrical path from current in the path and a voltage derived from the voltage present on the path.
These and many other objects, features and advantages of the invention will become evident from the following detailed description which is presented in conjunction with the accompanying drawings.